I think you may be treating Parker a little unfairly. Nobody was ever going to
be able to complete a Chandler novel successfully, and in particular that
Chandler novel.

I presume you've read that compilation of short stories featuring Philip Marlowe written by a number of mystery writers, including Dick Lochte, who's here on Rara Avis. some of course were more successful than others at capturing the feel and voice of Chandler, but to my recollection, a few did it quite well. who those guys were unfortunately escapes me now. but I remember that here on RA a number of years back, we read a different story from the compilation every week and commented on it

John Lau

"If you even dream of beating me you'd better wake up and apologize."
Muhammad Ali

I think you may be treating Parker a little unfairly. Nobody was ever going to
be able to complete a Chandler novel successfully, and in particular that
Chandler novel. The Chandler who began to write it was no longer the Chandler
of 'The Big Sleep' or 'Farewell My Lovely', just as the Parker who tried to
complete it no longer wrote like the guy in 'The Godwulf Manuscript' or 'Heaven
Help the Child', but had gone on to find his own voice, totally unlike the
Chandler tribute it had once been.
Perhaps if he had tried completing 'The Poodle Spring Story' earlier in his
career, things might have worked out differently, or at least less
unsatisfactorily.
I think that so much of Chandler's attraction lies in the actual writing and its
distinctively formed style that it would have taken a mimic of even greater
talent than the object of his mimicry to have had a chance of succeeding, and
even then...
How much, if any, of this applies to completing a Westlake novel I don't know,
as I have only read a couple of his Stark / Parker series and that was some
considerable time ago now; but whoever attempts it I wish him luck, a fair wind,
and even fairer critics.